Overview on hard part turning

What is Hard Part Turning?

Hard Part Turning is a fantastic alternative to Cylindrical grinding, and for the right component can have some great advantages. Turning steel with a hardness over 45 HRc (typically within the range of 55-68 HRc) is defined as hard part turning and is a cost efficient alternative to grinding. Since surface roughness of Rmax/Rz=1.6s can be achieved, hard turning is often considered a replacement for grinding operations or as a pre-grinding process.


What sort of components would benefit from hard part turning?  Typical parts are brake rotors, transmission gears, steering pinions, valve seats, pistons, cylinder liners and clutch housings. The “sweet spot” for hard turning applications are for parts that have roundness accuracy requirements between 0.8 and 12 microns, and surface roughness requirements between Rz 0.8 micron and Rz 7.0 microns.

Hard Part Turning has a number of advantages over cylindrical grinding. A turning center can complete ID turning, OD turning, taper turning, and grooving in a single chucking. It will also improve the accuracy of squareness, concentricity and straightness. Drastically reducing cycle and setup times as well. Our client Sandvik says it can “reduce machining time and costs by 70% or more.” Hard Turning also allows for the finishing of radius and free-curved surfaces. This is a distinct advantage over Grinding where either custom-dressed wheels (which are time consuming to produce) or highly customised grinding machines would be needed.


Grinding has the advantage of being able to achieve higher dimensional roundness and cylindricity accuracies compared with hard turning. However, since parts can typically be finished in a single chucking, hard turned parts often show superior concentricity and perpendicularity characteristics to their ground counterparts. Hard Part Turning has inherent advantages over grinding but requires specific knowledge and experience that not all machinists possess. Although it will save you money in the long run, the initial investment in CBN inserts is pretty steep.

In order to take full advantage of the benefits of Hard Part Turning without any learning curve or investment, why not outsource to a reliable sub-contract machinist like B&B Precision? Send through your RFQs today to: mail@bandbprecision.co.uk or call 01484 866386


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